1. Field of the Invention
The present invention relates to a ink jet print head. More specifically, it relates to an ink jet print head in which ink droplets are jetted out through orifices by increasing inner pressure of an ink chamber and fixed on a recording medium such as paper or transparent film, enabling very fine printing with high resolution.
2. Description of the Background Art
In a conventional ink jet printer disclosed in Japanese Patent Publication No. 53-12138/1978 (corresponding to U.S. Pat. No. 3,946,398), a piezo vibrator is provided facing an ink chamber, the piezo vibrator is deformed by applying an electric signal thereto so as to reduce volume of the ink chamber and increase inner pressure of the ink chamber, whereby an ink droplet is ejected from an orifice. In this method, it is necessary to provide piezo vibrators same in number as the corresponding ink ejecting channels (number of orifices). Therefore, it is difficult to reduce the size and highly dense arrangement of orifices is limited.
Ink jet print heads of other types include ones in which wall surface of an ink chamber is deformed inward to cause pressure to eject ink droplets by electrostatic force or magnetic force.
However, these methods suffer from problems that the generated pressure is too small or that the head becomes too large when necessary high pressure is to be generated.
FIG. 15 shows a schematic structure of a conventional serial print type ink jet printer. A pair of guiding rods 7 and 8 are provided parallel to a platen 6 around which a sheet of paper, not shown, is wound and fed. Along guiding rods 7 and 8, a carriage 4 is reciprocally attached. A head body 1 is mounted on carriage 4, and an ink tank 2 is mounted on body 1. Head body 1 ejects and fixes ink droplets onto the sheet of paper fed by platen 6, whereby printing is-done. Reference numeral 5 denotes a maintenance station.
FIG. 16 is a perspective view showing schematically a conventional serial print type ink jet print head. There is a nozzle 3 on the front end surface of head body 1 on which ink tank 2 is mounted.
FIG. 17 is a partially exploded perspective view showing, in enlargement, an internal structure of nozzle 3, and FIG. 18 is a cross section thereof. In nozzle 3, a number of mutually parallel partitions 15 are formed continuously and integrally from an inner bottom surface, a filter 12 is provided at a rear portion between adjacent ones of partitions 15, 15 and front end side of each partition 15 is formed to have a triangular plate shape 15a and faces a front surface of nozzle 3. An upper surface of the group of partitions 15 is covered and tightly sealed by a pressure chamber ceiling 16 which is integral with nozzle 3, and by adjacent partitions 15, 15, filter 12 and pressure chamber ceiling 16, a number of ink pressure chambers 11 are formed parallel to each other. Because of the triangular plate 15a, the front end side of each ink pressure chamber 11 is tapered, and opened as an orifice 10 at the front surface of nozzle 3. Behind the group of partitions 15 and the group of filters 12, there is formed a common ink feed path 13 surrounded by the inner bottom surface of nozzle 3 and pressure chamber ceiling 16. The common ink feed path 13 is communicated with ink tank 2 shown in FIG. 16 and receives ink supply from ink tank 2. Further, this ink feed path is communicated with each ink pressure chamber 11 with each filter 12 interposed, and supplies ink to each ink pressure chamber 11. A piezo vibrator 14 is bonded on an upper surface of pressure chamber ceiling 16 at a position corresponding to each ink pressure chamber 11. Between each piezo vibrator 14 and pressure chamber ceiling 16 which is at the ground potential, a series circuit including a power supply 17 and a switch 18 is connected individually.
The operation will be described in the following. As shown in FIG. 18, ink pressure chamber 11 is filled with ink 19. When switch 18 is off as shown in FIG. 18A, voltage is not supplied from power supply 17 to piezo vibrator 14. Accordingly, piezo vibrator 14 is not driven and hence it is kept flat. Therefore, inner pressure of ink pressure chamber 11 does not change, and equilibrium between each of ambient pressure, surface tension and ink pressure is kept at orifice 10. Accordingly, ink droplet is not ejected from orifice 10.
When switch 18 is turned on as shown in FIG. 18B, a voltage is supplied to piezo vibrator 14 from power supply 17, piezo vibrator 14 is deformed curved with the central portion projecting downward, pressure chamber ceiling 16 deforms curved downward with respect to ink pressure chamber 11 at a position corresponding to the driven piezo vibrator 14, a volume of the corresponding ink pressure chamber 11 reduces and inner pressure of ink pressure chamber 11 increases. As a result, ink 19 is forced out from orifice 10 as an ink droplet 19a, which jets toward a recording medium, not shown.
However, in the ink jet print head in accordance with the prior art shown in the figures, means for supplying ink uniformly to respective ink pressure chambers 11 from common ink feed path 13 is not provided. Therefore, the amount of ink 19 in respective ink pressure chambers 11 and hence inner pressure of these chambers differ from each other, and as a result, ink droplets 19a ejected from orifices 10 may have different sizes.
The present invention was made in view of the foregoing and its object is to provide an ink jet print head by which ink droplets ejected from all orifices are adapted to have approximately uniform size. A further object is to enable simple switching between ink droplet ejecting state and non-ejecting state. A still further object is to enable simple adjustment of the size of the ejected ink droplets.
According to an aspect of the present invention, the above described objects can be attained by an ink jet print head including a plurality of ink chambers partitioned from each other, each having, at a front end portion, an orifice; a common pressure chamber connected to the plurality of ink chambers through a first filter; a common ink feed path connected to the common pressure chamber through a second filter; a pressure generating member provided on a wall surface of the common pressure chamber; and a movable wall provided in each of the plurality of ink chambers and deformable in a direction increasing volume of the ink chamber; in which a pressure wave generated by the drive of the pressure generating member in the common pressure chamber is transmitted to each of the plurality of ink chambers through the first filter, which pressure wave is absorbed when the movable wall is deformed, and it causes an ink droplet to be ejected from the orifice when the movable wall is not deformed.
Preferably, the pressure generating member of the ink jet print head is driven periodically, and whether the ink droplet is to be ejected or not is switched by changing timing of deformation of the movable wall in the direction increasing the volume of the ink chamber with respect to the timing of driving the pressure generating member.
More preferably, the ink jet print head adjusts the size of the ejected ink droplets by changing the timing of deformation of the movable wall in the direction increasing the volume of the ink chamber with respect to the timing of driving the pressure generating member when the ink droplets are to be ejected.
More preferably, the ink jet print head further includes a highly resilient member for receiving deformation of the movable wall.
In accordance with the present invention, the common pressure chamber is separated from the common ink feed path by the second filter, and pressure wave generated by driving the pressure generating member in the common pressure chamber is supplied to each of the ink chambers through the first filter. Therefore, the amount of ink and inner pressure are uniform in every ink chamber. Accordingly, when the pressure wave from the common pressure chamber is received by the ink chambers, the ink droplets ejected from the orifices come to have uniform size.
Further, the pressure generating member is driven periodically, and by changing the timing of deformation of the movable wall in the direction increasing the volume of the ink chamber with respect to the timing of driving the pressure generating member, it is possible to switch ejection/non-ejection of ink droplets. Therefore ink droplets can be controlled in a simple manner.
Further, when the ink droplets are ejected, by changing the timing of deformation of the movable wall in the direction increasing the volume of the ink chamber with respect to the timing of driving the pressure generating member, the size of the ejected ink droplet can be adjusted. Therefore, the size of the ink droplet can be adjusted in a simple manner.
Further, a highly resilient member receiving deformation of the movable wall is provided, and therefore the movable wall deformed by the pressure wave can be received by the highly resilient member. Accordingly, parasitic vibration or undesirable deformation of movable wall by the pressure wave can be avoided, and ejection/non-ejection of ink droplets can be controlled stably.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.